harmonize mouse tracking with other TEs #4582
Description
Coming from #4581.
We should try to establish the same mouse tracking behavior as seen on other TEs:
- UP & DRAG should be triggered from outside of the terminal area, if DOWN originates from within the terminal
- coords should be clamped to the outermost position still within the terminal area
- UP should always be triggered within the terminal area (fixing w3m bug)